The invention disclosed herein relates to a method and device for splicing webs on which labels are printed so as to provide an uninterrupted supply of labels to a machine which applies labels to containers such as bottles and cans.
A known method and device for splicing the leading end of a web fed from a standby spool or reel to the trailing end of a web fed from an alternative active storage spool on which the supply web is nearly exhausted is described in German DE-OS 31 09 529. This known device features a grooved web cutting drum and two gluing drums. The cutting drum can be adjusted with respect to the web supply spool or reel and one of the gluing drums can be lowered such that it can be tangential to the cutting groove drum and the other glue drum. A cutting device that is moved perpendicular to the label web toward the grooved cutting drum is associated with the grooved cutting drum. At least two rollers that deflect or change the direction of the label web are arranged between the splicing device and the supply spool. A scanning device that scans the label image printed on the web is associated with the supply spool and is upstream of the splicing device in order to properly position the splice. To achieve this, a drive roller swivels toward the full supply spool and simultaneously the grooved cutting drum is swiveled tangentially to the supply spool, and one of the other gluing drums is swiveled tangentially to the grooved cutting drum and the other gluing drum. The leading end of the replacement web that belongs to the supply spool adheres firmly to the grooved cutting drum when it is sufficiently proximate to the full supply spool and is transferred from there to a splicing position that is properly positioned and parallel to the web that is near depletion with the aid of the scanning devices. Following such positioning, the leading end of the replacement web or substitute web and the end of the presently running web are cut by means of a cutting device, whereby the section of the leading end of the web located behind the cutting position is held on the grooved cutting drum by means of a vacuum bar. Further rotation of the grooved cutting drum brings about application of adhesive tape in succession to both sides of the line where cutting is done by means of the gluing drum, so that the trailing and leading ends of the respective nearly consume and substitute webs are adhered flush with each other. After the splicing has been completed, the full supply spool is swiveled into position away from the grooved cutting drum.
The disadvantages of the method just outlined is complicated in its implementation and the implementation device has a complicated design. Furthermore, a properly positioned splice apparently can only be achieved with difficulty, since slippage of the leading end of the replacement web that is merely glued to the grooved cutting drum can occur as a result of the high acceleration of the web to match the momentary speed of the web which is about to become depleted or run out. Slippage between the leading end of the web and the grooved cutting drum is more often the rule than the exception. With the known procedure, flush gluing is only possible with strips of adhesive tape. These strips are applied to both sides of the web, which, at least on the outer part of the web, or the visible surface of the web, is not desirable from an aesthetic point of view. Splicing with liquid adhesives is not possible in this known design. Furthermore, cutting of the web takes place prior to connecting the leading end of the replacement web to the trailing end of the expiring web, whereupon relatively significant mechanical effort is expended. It is also disadvantageous that the cutting device used to cut through the web undergoes a movement transverse to the direction of the motion of the web, and must engage in a cutting groove on the grooved cutting drum. Carrying out splicing on a labeling machine operating under normal conditions, therefore, does not appear to be possible. In the web splicing method and device disclosed in German DE OS 24 56 342 the leading end of the replacement web is maintained in a state of readiness by a vacuum drum and is transferred into the splicing position parallel to the end of the web that is running out. Slippage of the leading end of the web on the drum due to high accelerating forces and the large moment of inertia of the web supply spool, cannot be avoided, so a properly positioned splice is not assured under all conditions. There is also a danger after cutting both the expiring web and the replacement web, the web that faces the cutting drum will stick out tangent to the drum as a result of the curvature of the cutting drum, so that flush gluing of the web at the cutting point is more difficult and, perhaps, not even possible.
A method and device are also known from European patent application EP-A2 0 273 286 wherein the webs can be connected flush with each other by means of strips of adhesive tape. Because a movable gluing block is provided in this case and is perpendicular to the direction in which the web is being withdrawn, the splicing of the label webs is, if at all, only possible at low web withdrawal speeds.